Printer Mechanism Operation; Printhead Mechanism - Epson LQ-1170 Service Manual

2.1 PRINTER MECHANISM OPERATION

This section describes the Model 5D 10/5D60 printer mechanism and explains how it works. The Model
5D 10\5D60 printer mechanism features a 24-pin impact dot printhead for serial printing. The printer
mechanism has four main parts: the printhead mechanism, the carriage movement mechanism, the paper
advance mechanism, and the ribbon advance mechanism. The following sections describe these parts.

2.1.1 Printhead Mechanism

The printhead mechanism consists of the printhead itself, the ink ribbon, and the platen. The printhead
contains 24 wires in a zigzag arrangement in two rows of 12. A drive coil is provided for each of these
wires to make the wires move in and out of the printhead and print dots independently of each other.
The four steps below describe the basic way that the wires are driven.
1. The control circuit outputs the drive signal to the printhead drive circuit. This changes the printhead
drive voltage and current flows through the corresponding printhead coil. The coil acts as a solenoid
and generates a magnetic force.
2. This induced force causes the plate to approach the coil rod and the associated dot wire is rapidly
ejected to impact on the platen.
3. The dot wire presses the ink ribbon up against the paper as it hits the platen and, in this way, prints
a dot on the paper.
4 As soon as the current through the coil is switched off, the force induced in the coil rod stops. The
plate then returns to its original position (its position before the coil was energized) through the action
of the plate spring. After the dot wire hits the platen, the rebounding force of hitting the platen works
with the wire return spring to pull the wire back to its original position in relation to the plate.
Wwe Resetting Spring
Stopper
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f
Actuating Plate ~
l
Act~ating Plate Spring
Figure 2-1 shows how the printer mechanism prints a single dot.
The printhead tends to heat up after a period of continuous printing. To minimize the possibility of the
dot wire drive coils in the printhead overheating and causing a loss of performance, the printhead is
equipped with a thermistor that detects the temperature of the printhead. When this thermistor detects
changes in the printhead temperature, the voltage signal changes. The control circuit reads this signal
change for feedback control.
Dot Wwe
4
~ ~
l x l
Figure 2-1. How the Printhead Works
Ribbon Mask
" ~
Y
Ribbon
Paper
2-1
REV.-A
Platen